Note 9 - Cash, Cash Equivalents, Investments and Restricted Cash - Unrealized Gains and Losses on Investments (Details) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Adjusted Cost	$ 254,165	$ 230,585
Total Fair Value	251,756	229,221
Unrealized Gains	10	17
Unrealized Losses	(2,419)	(1,381)
Fair Value of Investments in Unrealized Loss Position	231,429	215,844
Money Market Funds [Member]
Adjusted Cost	16,081	7,134
Total Fair Value	16,081	7,134
Corporate Debt Securities [Member]
Adjusted Cost	209,385	204,789
Total Fair Value	207,461	203,807
Unrealized Gains	10	17
Unrealized Losses	(1,934)	(999)
Fair Value of Investments in Unrealized Loss Position	203,215	197,564
US Government Agencies Short-term Debt Securities [Member]
Adjusted Cost	23,129	13,092
Total Fair Value	22,967	13,024
Unrealized Losses	(162)	(68)
Fair Value of Investments in Unrealized Loss Position	22,967	13,024
Auction Rate Securities [Member]
Adjusted Cost	5,570	5,570
Total Fair Value	5,247	5,256
Unrealized Losses	(323)	(314)
Fair Value of Investments in Unrealized Loss Position	$ 5,247	$ 5,256

Amount of investment in debt and equity securities categorized neither as held-to-maturity nor trading.

No definition available.

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- Definition

Amount before tax of unrealized gain in accumulated other comprehensive income (AOCI) on investments in debt and equity securities classified as available-for-sale.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27161-111563

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- Definition

Amount before tax of unrealized loss in accumulated other comprehensive income (AOCI) on investments in debt and equity securities classified as available-for-sale.

+ References

No definition available.

+ Details

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- Definition

This item represents the cost of debt and equity securities, which are categorized neither as held-to-maturity nor trading, net of adjustments including accretion, amortization, collection of cash, previous other-than-temporary impairments recognized in earnings (less any cumulative-effect adjustments recognized, as defined), and fair value hedge accounting adjustments, if any.

+ References

No definition available.

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- Definition

This item represents the aggregate fair value of investments in debt and equity securities in an unrealized loss position which are categorized neither as held-to-maturity nor trading securities.

+ References

No definition available.

+ Details

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